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Street lights as artificial stars

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#1 wonderweb

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Posted 28 July 2021 - 11:47 AM

Hi.

I have been trying to get my rc6 collimated as well as possible and am looking at different methods of producing artificial stars so I can spend cloudy nights getting it set up properly to maximise my image capture time when its clear and I was wondering if it was possible to use very distant street lights for this purpose? I am able to see street lights at a distance of around 10 to 15 miles. Is this far enough to work?

Thanks

#2 MisterDan

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Posted 28 July 2021 - 12:13 PM

Since your goal is strictly collimation, your primary considerations (and "tools") are the intra- and extrafocal Fresnel patterns.  If the light source generates bright, clear, sharp images of the Fresnel patterns and secondary shadow, and they allow you to "see" and determine relative alignment/misalignment, then they will work just fine.

 

Best wishes.

Dan



#3 lee14

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Posted 28 July 2021 - 12:50 PM

High magnification of the light source, ideally a point source, will give the best results. Diffraction patterns inside and outside of focus are useful for examining the optical quality of the system, but not necessary for collimation. A bright point, defocused to show the shadow of the secondary, is the goal. Center the spot within the image of the source and you're there. You can use any pinpoint source during the day, a sufficiently distant (far enough away to achieve focus) mirror ball is often cited as suitable. Or a pinhole in a piece of cardboard, illuminated by bright light, will also be fine on a cloudy night (or just in the dark).

 

Lee



#4 rhetfield

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Posted 28 July 2021 - 03:39 PM

Hi.

I have been trying to get my rc6 collimated as well as possible and am looking at different methods of producing artificial stars so I can spend cloudy nights getting it set up properly to maximise my image capture time when its clear and I was wondering if it was possible to use very distant street lights for this purpose? I am able to see street lights at a distance of around 10 to 15 miles. Is this far enough to work?

Thanks

You will just have to try it and see if it is a good enough point source.  At that distance, I would think that there is a good chance.



#5 JIMZ7

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Posted 29 July 2021 - 09:39 PM

I used street lights & Christmas lights for decades to test reflectors & refractors performances with many eyepieces.

Jim



#6 a__l

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Posted 29 July 2021 - 10:00 PM

Hi.

I have been trying to get my rc6 collimated as well as possible and am looking at different methods of producing artificial stars so I can spend cloudy nights getting it set up properly to maximise my image capture time when its clear and I was wondering if it was possible to use very distant street lights for this purpose? I am able to see street lights at a distance of around 10 to 15 miles. Is this far enough to work?

Thanks

10-15 miles far and low above the horizon. The atmosphere will be turbulent.
Better something closer and high above the ground. For example, lanterns on high television tower or tall buildings.


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#7 ram812

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Posted 29 July 2021 - 11:56 PM

Or a tall radio tower beacon.

#8 Asbytec

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Posted 30 July 2021 - 07:42 AM

You can use a streetlight, sure, but try to find a reflected glint of the street light nearby. I would not use the street light itself. You can even do this during the day by finding a glint of sunlight off of something reflective. A car bumper might work. I used my neighbors roof shingles, it has some small shiny stones embedded in them. As mentioned, Christmas tree bulbs work. A shiny ball bearing. Anything, really, including a tall radio tower. 


Edited by Asbytec, 30 July 2021 - 07:44 AM.

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#9 George N

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Posted 30 July 2021 - 02:40 PM

I remember reading an article about John Dobson and a friend making a 24-inch mirror in a single long weekend - working straight thru - no sleeping - just eating. When they got to figuring - they used a distant streetlight for most of the testing. John had a knack to know what was wrong with a mirror and how to fix it - just from a quick 'star' test -- make that 'street light test' in a pinch.



#10 Orion68

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Posted 30 July 2021 - 04:49 PM

I've seen a star test complete with diffraction rings using my Questar to view dew drops sitting tree leaves in my yard. Was quite surprised!


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#11 cuzimthedad

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Posted 31 July 2021 - 10:04 AM

Moving to Cats & Casses



#12 lphilpot

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Posted 31 July 2021 - 04:24 PM

Better something closer and high above the ground. For example, lanterns on high television tower or tall buildings.

Being guyed, I wonder if the slight swaying of a radio / TV tower might make it difficult to stay centered?



#13 a__l

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Posted 31 July 2021 - 07:14 PM

The visual amplitude of the angle depends on the distance.  I don't think this is a problem at a sufficient distance. It is important for you that the light source is close to a dot.
Even if there are small fluctuations of low frequency, which you will be able to notice (which I doubt) will not somehow prevent you from collimating the telescope.

 

Ps. I don't think you will be comfortable doing collimation in high winds. Your telescope will vibrate significantly more.


Edited by a__l, 31 July 2021 - 07:29 PM.



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